1. Field of the Invention
The present invention relates to methods of treating subterranean zones using high density viscous salt water treating fluids.
2. Description of the Prior Art
High density viscous salt water treating fluids are often used in operations and treatments conducted in oil and gas wells. Such operations and treatments include, but are not limited to, well completion operations and production stimulation treatments.
An example of a well completion operation in which a high density viscous salt water treating fluid is often used is gravel packing. In gravel packing operations, particulate material referred to in the art as gravel, is carried to a subterranean zone in which a gravel pack is to be placed by a viscous treating fluid. That is, particulate material such as sand is suspended in the viscous treating fluid at the surface and carried to the subterranean zone in which a gravel pack is to be placed. Once the particulate material utilized is placed in the zone, the viscous treating fluid breaks into a low viscosity fluid. The gravel pack produced functions as a filter to separate formation solids from produced fluids while permitting the produced fluids to flow into and through the well bore.
An example of a production stimulation treatment in which a high density viscous salt water treating fluid can be used is hydraulic fracturing. That is, a viscous treating fluid referred to in the art as a fracturing fluid, is pumped through the well bore into a subterranean zone to be stimulated at a rate and pressure such that fractures are formed and extended in the subterranean zone. At least a portion of the fracturing fluid carries particulate material such as sand, referred to in the art as proppant, into the formed fractures. The proppant is suspended in the viscous aqueous fracturing fluid so that the proppant is deposited in the fractures when the pumping stops and the fractures close onto the proppant. The proppant functions to prevent the formed fractures from completely closing whereby conductive channels are formed through which produced fluids can flow to the well bore.
In the completion or stimulation of oil and gas wells and particularly in off shore wells having relatively low temperatures, i.e., temperatures in the range of from about 80° F. to about 140° F., high density viscous salt water treating fluids having densities in the range of from about 9 lbs/gal to about 15 lbs/gal are often required for well control purposes. In addition, the viscous salt water treating fluid must maintain viscosity for at least about two to three hours and must be completely broken in a few days. Because of the low temperatures and the high salt concentrations in the high density viscous salt water treating fluids utilized heretofore, the oxidizing viscosity breakers utilized have often failed to completely break the salt water treating fluid viscosities in the required times. Thus, there are continuing needs for improved high density viscous salt water treating fluids that break, i.e., are reduced to low viscosity fluids, in relatively short periods of time at low temperatures. The time required, either a matter of hours or days, will depend on the treatment design.